my sand is a hayward SP0714T SERIES VARI-FLO XL VALVE,Yes I can backwash rince with no ploblem.Here is what I did,I unhooked my new filter,and hooked up my old 100lb filter,and it does the sand thing.didnt do anything different,and last yr this work great,this is why I'm so puzzled.and frustrated.And now I have another problem,I have a leak in my liner.so Im trying to find another liner.I will keep you all posted
thank for all your help